[clang] 05b8a36 - [Clang][Diagnostics] Mention 'import std' in typeid diagnostic (#173236)

[via cfe-commits]

Author: Yuki
Date: 2026-01-05T02:23:10Z
New Revision: 05b8a36f1b542ae903cac11de1bbb26695b7fdac

URL: https://github.com/llvm/llvm-project/commit/05b8a36f1b542ae903cac11de1bbb26695b7fdac
DIFF: https://github.com/llvm/llvm-project/commit/05b8a36f1b542ae903cac11de1bbb26695b7fdac.diff

LOG: [Clang][Diagnostics] Mention 'import std' in typeid diagnostic (#173236)

Previously, the diagnostic only suggested including `<typeinfo>`. Since
C++20,the standard library may also be made available via `import std;`.

This change updates the diagnostic to mention `import std` as an
alternative and adds a test to cover the new wording.

Added: 
    clang/test/SemaCXX/typeid-requires-typeinfo.cpp

Modified: 
    clang/include/clang/Basic/DiagnosticSemaKinds.td
    clang/lib/Sema/SemaExprCXX.cpp

Removed: 
    


################################################################################
diff  --git a/clang/include/clang/Basic/DiagnosticSemaKinds.td b/clang/include/clang/Basic/DiagnosticSemaKinds.td
index 6c6a26614ad0e..4f7934b328d9f 100644
--- a/clang/include/clang/Basic/DiagnosticSemaKinds.td
+++ b/clang/include/clang/Basic/DiagnosticSemaKinds.td
@@ -8429,7 +8429,7 @@ def err_bad_dynamic_cast_not_polymorphic : Error<"%0 is not polymorphic">;
 
 // Other C++ expressions
 def err_need_header_before_typeid : Error<
-  "you need to include <typeinfo> before using the 'typeid' operator">;
+  "you need to include <typeinfo>%select{| or import std}0 before using the 'typeid' operator">;
 def err_need_header_before_placement_new : Error<
   "no matching %0 function for non-allocating placement new expression; "
   "include <new>">;

diff  --git a/clang/lib/Sema/SemaExprCXX.cpp b/clang/lib/Sema/SemaExprCXX.cpp
index 965ad55465db7..91967a7a9ff97 100644
--- a/clang/lib/Sema/SemaExprCXX.cpp
+++ b/clang/lib/Sema/SemaExprCXX.cpp
@@ -644,8 +644,10 @@ Sema::ActOnCXXTypeid(SourceLocation OpLoc, SourceLocation LParenLoc,
   }
 
   // Find the std::type_info type.
-  if (!getStdNamespace())
-    return ExprError(Diag(OpLoc, diag::err_need_header_before_typeid));
+  if (!getStdNamespace()) {
+    return ExprError(Diag(OpLoc, diag::err_need_header_before_typeid)
+                     << (getLangOpts().CPlusPlus20 ? 1 : 0));
+  }
 
   if (!CXXTypeInfoDecl) {
     IdentifierInfo *TypeInfoII = &PP.getIdentifierTable().get("type_info");
@@ -659,7 +661,8 @@ Sema::ActOnCXXTypeid(SourceLocation OpLoc, SourceLocation LParenLoc,
       CXXTypeInfoDecl = R.getAsSingle<RecordDecl>();
     }
     if (!CXXTypeInfoDecl)
-      return ExprError(Diag(OpLoc, diag::err_need_header_before_typeid));
+      return ExprError(Diag(OpLoc, diag::err_need_header_before_typeid)
+                       << (getLangOpts().CPlusPlus20 ? 1 : 0));
   }
 
   if (!getLangOpts().RTTI) {

diff  --git a/clang/test/SemaCXX/typeid-requires-typeinfo.cpp b/clang/test/SemaCXX/typeid-requires-typeinfo.cpp
new file mode 100644
index 0000000000000..ee6efada474b0
--- /dev/null
+++ b/clang/test/SemaCXX/typeid-requires-typeinfo.cpp
@@ -0,0 +1,10 @@
+// RUN: %clang_cc1 -triple %itanium_abi_triple -fsyntax-only -verify=cxx20 -std=c++20 %s
+// RUN: %clang_cc1 -triple %itanium_abi_triple -fsyntax-only -verify=cxx17 -std=c++17 %s
+
+class A{};
+
+auto f() {
+  // cxx20-error at +2 {{you need to include <typeinfo> or import std before using the 'typeid' operator}}
+  // cxx17-error at +1 {{you need to include <typeinfo> before using the 'typeid' operator}}
+  return typeid(A);
+}